1. Field of the Invention
The present invention relates to an electrically operated fuel pump device mounted on vehicles for forcedly delivering liquid fuel from a fuel reservoir to a fuel consumption installation at high pressure and at low flow rate.
2. Description of the Prior Art
An electrically operated fuel pump device used to forcedly deliver liquid fuel within a fuel tank to an engine of vehicles, for example, is required to supply the fuel at a relatively high discharge pressure of 2-3 Kg/cm.sup.2 and at a relatively low discharge flow rate of 40-150 l/hr. Therefore, most of such fuel pump devices utilize a positive displacement pump. There are also fuel pump devices using a centrifugal pump. However, the use of such fuel pump devices is limited to a case where the fuel is delivered at a relatively low discharge pressure below 1 Kg/cm.sup.2.
The fuel pump device which utilizes the positive displacement pump has such disadvantages that the manufacturing cost is high, because a desired performance is not obtained as far as the manufacturing accuracy or tolerance is not increased, and that vibration and noise are increased because of high fluctuation in discharge pressure. In addition, the fuel pump device utilizing the centrifugal pump can obtain low pressure and high flow rate, but is difficult to obtain high pressure and low flow rate.
The inventors of the present application have directed their attention to the use of a closed vane type regenerative pump or WESTCO pump as a pump for the fuel pump device. It is possible for the regenerative pump to obtain a discharge pressure of order of 2-3 Kg/cm.sup.2. However, if the regenerative pump is designed by the introduction of the generally used design factors or requirements of conventional regenerative pumps as they are, sufficient high discharge pressure is obtained, but discharge flow rate is increased more than is necessary. Accordingly, it is inappropriate to apply the generally used design factors or requirements to a regenerative pump of the fuel pump device for vehicles. The forced reduction of the discharge flow rate to a required level causes the pump efficiency to be considerably decreased. An electric motor for actuating the pump is required to have large capacity to increase the motor output so that the entire fuel pump device is large-sized and the consumed electric power is increased.